The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2000-358726, filed on Nov. 27, 2000. The contents of that application are incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a rotary pump apparatus that has a plural number of discharge ports.
2. Discussion of the Background
A conventional vane-type rotary pump apparatus is composed of a stator housing, a cam ring formed at its inner periphery with a cam surface radially offset from its central axis and mounted within the stator housing, a pair of end wall structures fitting to the opposite ends of the cam ring to form a pump cavity in the cam ring, a drive shaft rotatably mounted within the stator housing and extending into the interior of the pump cavity through one of the end wall structures, a rotor contained within the cam ring and mounted on the drive shaft for rotation therewith, and a plurality of cireumferentially equally spaced vanes slidably fitted into a body of the rotor to move radially outward from the rotor and cooperating with the cam surface of the cam ring to form a plurality of expandable pump chambers. FIG. 1 is a cross-sectional view of a conventional pump apparatus. As shown in FIG. 1, the pump apparatus, called a balance-type pump, has an even number (typically two) of discharge ports 91, 92 that open in a ring shape pressure chamber 93. Operating fluid pumped at the pump chambers flows into the pressure chamber 93 through the discharge ports 91, 92 and flows out from the pressure chamber 93 to a flow control valve through an outflow passage 94.
The operating fluid that flows into the pressure chamber 93 from the discharge port 91, which is disposed close to the outflow passage 94, is divided into two streams as it flows to the outflow passage 94. These are a stream flowing clockwise as shown by solid arrows in FIG. 1 and a stream flowing counterclockwise as shown by a dotted arrow in FIG. 1 in the ring shaped pressure chamber 93. The counterclockwise stream collides with the clockwise stream and a stream that flows from the other discharge port 92 near an opening of the outflow passage 94. As a result, these streams create a turbulent flow near the opening of the outflow passage 94. This turbulent flow causes cavitation in the outflow passage 94, which prevents the stable supply of operating fluid to the flow control valve.
In view of the foregoing, it is an object of the present invention to provide an improved rotary pump apparatus. In order to achieve the above and other objects, the present invention provides a rotary pump apparatus which comprising a stator housing, a pump, at least two discharge ports, a ring shaped pressure chamber, an outflow passage and an interception wall. The pump is contained in the stator housing. The discharge ports discharge the operation fluid from the pump, and are opened in the ring shaped pressure chamber. The pressure chamber is formed in the stator housing and is defined by an outer wall and an inner wall. The outflow passage is opened into the pressure chamber. The interception wall is formed in the pressure chamber by connecting one portion of the outer wall and one portion of the inner wall. Since the interception wall is formed in a ring shaped pressure chamber, the operation fluid is rectified in the ring shaped pressure chamber and flows out to the outflow passage in a condition of laminar flow. Therefore, the operation fluid can be supplied to an outside device in a stable state.
Preferably, the interception wall is formed to prevent the operation fluid streams from flowing either clockwise or counterclockwise in the ring shaped pressure chamber. Further, it is preferable that the interception wall is formed between the opening portion of the outflow passage and one of the opening portions of discharge ports which is the nearest to the outflow passage. Furthermore, it is preferable that interception wall is formed adjacent the opening of the outflow passage.